The invention relates to a support element of an automatic load platform of a silicon wafer exposure unit, which element has a circular cross-section with a first outer diameter which is adapted to the guide of a load station and which is smaller than that of a silicon wafer.
Known automatic load platforms for exposure units such as the UT-stepper of the Ultratech Company, USA, have a circular disc as a support element (chuck) on the load platform whose greatest diameter is smaller than that of the silicon wafer to be exposed. The greatest width of the support element is limited in that case by the width of an insertion slot leading into the load station, i.e. into a station in which the load platform or the support element is loaded with a silicon wafer, which is usually done automatically. After the silicon wafer has been positioned on the load platform, the load platform moves to below an exposure station, which usually comprises a light source and a mask which generates a sharp image on the silicon wafer to be illuminated. Since the silicon wafer projects beyond the edge of the support element, the silicon wafer is supported imperfectly in the edge region, so that it exhibits an overall curvature which leads to a defocusing of approximately 5 to 20 .mu.m at the edge of the silicon wafer. As a result, the rejection rate in the exposure process of such silicon wafers lies at 30 to 40%, which strongly detracts from the manufacturing process.